The random orientation of fibers in unoriented nonwoven fabrics provides such fabrics with a variety of useful properties and characteristics. One of these characteristics is the ability of such fabrics to resist continued linear tearing in the cross direction after introduction of an initial tear in the fabric. While this resistance-to-split characteristic of nonwoven fabrics is a beneficial attribute for various applications, it presents certain difficulties when nonwoven fabrics are used as the backing of adhesive tapes such as surgical tapes which are dispensed from a roll.
If the nonwoven backing is of sufficiently low strength, the tape can be torn by hand without much difficulty. U.S. Pat. No. 3,121,021 issued to Copeland and assigned to the Minnesota Mining & Manufacturing Company of St. Paul, Minn. describes such low-strength nonwoven adhesive medical tapes. The tapes disclosed by Copeland possess a tensile strength of about six pounds per inch width (1071 grams/cm). Although they can be torn by hand, these tapes tend to tear unevenly.
Tapes made with high-strength nonwoven backings, such as SONTARA.TM. fabrics are widely believed to be too tear resistant to be torn by hand and must be cut to size by scissors or other cutting tools. Nonwoven surgical tapes of this type are available in continuous roll form with a release liner laminated to the adhesive side of the tape. The liner serves to enhance the mechanical integrity of the web during the unwinding process and to facilitate cutting with scissors. The desired length of surgical tape is dispensed from the roll by unwinding the desired length and cutting through both the surgical tape and the liner with a pair of scissors. The liner is then peeled from the surgical tape to expose the adhesive and the tape applied to the patient. This method of dispensing is significantly more cumbersome than dispensing by hand-tearing from a linerless roll.
High-strength linerless nonwoven surgical tape has recently become available to health care professionals as precut pads with a nonadhesive separation tab positioned along one edge of each layer. Such pads of precut surgical tape are available from Minnesota Mining and Manufacturing Company of St. Paul, Minn. as MEDIPORE.TM. dressing covers. A single layer of surgical tape is dispensed from the pad by simply gripping the nonadhesive tab attached to the top layer of surgical tape and peeling the top layer from the pad. The surgical tape is then applied to the patient and the tab peeled away. MEDIPORE.TM. dressing covers have significantly improved the ease of dispensing surgical tape by eliminating the need for scissors and have reduced the amount of waste by significantly reducing the amount of release liner required.
However, despite the advances provided by MEDIPORE.sup.TM pre-cut dressing covers, a need still existed for a completely linerless and tabless nonwoven surgical tape in roll form which could be dispensed without the need for scissors or other cutting tools and which tears cleanly and evenly.
One approach to providing a tearable nonwoven web is disclosed in Greenway, U.S. Pat. No. 4,772,499. Greenway suggests applying binder to the nonwoven web in spaced linear bands so that the web can be torn in a linear fashion along the binder-free bands of web. Unfortunately, the cost of producing such a banded nonwoven web is prohibitive for many purposes and differences in the surface characteristics of the web as between the binder-free and binder-containing bands would significantly complicate manufacture of the web and it is perceived that it would detract from the performance of the tape.
Patent Cooperation Treaty Publication WO 93/15245 filed by the Minnesota Mining and Manufacturing Company of St. Paul, Minn. discloses an embossed nonwoven tape including both staple and binder fibers. The specific composition of the tape in combination with the embossed pattern on the tape renders the tape tearable in the cross-machine direction along an embossed pattern in the tape. The tearable tapes disclosed by this publication are limited to those which include a significant proportion of melt-activated binder fibers.